Anaerobic Stabilization Ponds Research Articles

Occurrence, distribution, and fate evaluation of endocrine disrupting compounds in three wastewater treatment plants with different treatment technologies in Türkiye

Nowadays, two of the endocrine disrupting compounds (EDCs) in the group of alkylphenols (APs), nonylphenol (4-NP) and octylphenol (4-t-OP), have attracted great scientific and regulatory attention mainly due to concerns about their aquatic toxicity and endocrine disrupting activity. This paper investigated the occurrence, distribution behavior, fate, and removal of 4-NP and 4-t-OP in liquid and solid phases of three full-scale wastewater treatment plants (WWTPs) with different treatment technologies comparatively. In this context, (i) advanced biological WWTP, (ii) wastewater stabilization pond (WSP), and (iii) constructed wetland (CW) were utilized. In all three investigated WWTPs, the concentrations of 4-NP (219.9–19,354.4 ng/L) in raw wastewater were higher than those of 4-t-OP (13.9–2822.4 ng/L). Within the scope of annual average removal efficiencies, 4-NP was treated highly in advanced biological WWTP (93.5 %), while it was almost not treated in WSP (3.1 %) and treated with negative removal (<0 %) in CW. While 4-t-OP was treated at a similar removal rate (93.5 %) to 4-NP in advanced biological WWTP, it was treated moderately in WSP (52.5 %) and very poorly in CW (12.4 %). It has been determined that the most important removal mechanism of both 4-NP and 4-t-OP in WWTPs is biodegradation, followed by sorption onto sewage sludge. According to the mass balance performed in advanced biological WWTP, the biodegradation rates for 4-NP and 4-t-OP were found to be 70.4 % and 86.6 %, respectively, while the sorption onto sewage sludge were determined to be 23.3 % and 6.8 %. One of the critical findings obtained within the scope of the study is that while the concentrations of both metabolites, especially 4-NP, in wastewater and sewage sludge, decreased considerably under aerobic conditions, on the contrary, their concentrations increased significantly under anaerobic conditions. Both compounds were detected at higher concentrations in primary sludge compared to secondary sludge in advanced biological WWTP, while in WSP, they were determined at higher concentrations in anaerobic stabilization pond sludge compared to facultative stabilization pond sludge. Besides, it was also determined that the sorption behavior of these alkylphenols is much more dominant than desorption.

Mathematical modeling to size anaerobic stabilization ponds intended for slaughterhouse wastewater treatment – the role of temperature and hydraulic retention time

A new mathematical model for constructing anaerobic stabilization pond treatment systems for high organic load wastewater, based on biochemical oxygen demand, temperature and hydraulic retention time, is discussed.

Methane Emissions from Municipal Wastewater Collection and Treatment Systems.

Municipal wastewater collection and treatment systems are critical infrastructures, and they are also identified as major sources of anthropogenic CH4 emissions that contribute to climate change. The actual CH4 emissions at the plant- or regional level vary greatly due to site-specific conditions as well as high seasonal and diurnal variations. Here, we conducted the first quantitative analysis of CH4 emissions from different types of sewers and water resource recovery facilities (WRRFs). We examined variations in CH4 emissions associated with methods applied in different monitoring campaigns, and identified main CH4 sources and sinks to facilitate carbon emission reduction efforts in the wastewater sector. We found plant-wide CH4 emissions vary by orders of magnitude, from 0.01 to 110 g CH4/m3 with high emissions associated with plants equipped with anaerobic digestion or stabilization ponds. Rising mains show higher dissolved CH4 concentrations than gravity sewers when transporting similar raw sewage under similar environmental conditions, but the latter dominates most collection systems around the world. Using the updated data sets, we estimated annual CH4 emission from the U.S. centralized, municipal wastewater treatment to be approximately 10.9 ± 7.0 MMT CO2-eq/year, which is about twice as the IPCC (2019) Tier 2 estimates (4.3-6.1 MMT CO2-eq/year). Given CH4 emission control will play a crucial role in achieving net zero carbon goals by the midcentury, more studies are needed to profile and mitigate CH4 emissions from the wastewater sector.

Limnological Investigations of Sewage Stabilization Ponds at Sewage Treatment Plant in Bikaner (NW Rajasthan)

Abstarct: Geographically Bikaner has four natural slopes, one towards the vallabh garden area, where the three anaerobic and two aerobic stabilization ponds of sewage treatment plant are situated in the North –West part of the Rajasthan. The Thar desert lies which is characterized by typical arid conditions like scarcity of water, low rainfall, intense radiations, violent winds, high temperature fluctuations and dust storms. This paper is based on the chemical limnological study of three anaerobic and two aerobic stabilization ponds of sewage treatment plant. The study was carried out for a period of 15 months from March 2010 to May 2011. The chemical parameters measured include pH, EC (electrical conductance), TDS (total dissolve solids), and Free CO2. The parameters of three anaerobic stabilization ponds of water was ranged pH (6.7 to 8.2), EC (1.5 mmhos/cm to 2.0 mmhos/cm), TDS (960 mg/l to 1280 mg/ l), Free CO2 (172 mg/l to 294 mg/l) and two aerobic stabilization ponds of water was ranged pH (7.3 to 8.4), EC (1.3 mmhos/cm to 1.8 mmhos/cm), TDS (832 mg/l to 1152 mg/ l) and Free CO2 (152 mg/l to 270 mg/l) were recorded.

Fate of four Different Classes of Chemicals Under Aerobic and Anaerobic Conditions in Biological Wastewater Treatment

The removal mechanisms and extent of degradation of 28 chemicals (triclosan, fifteen polycyclic aromatic hydrocarbons, four estrogens, and eight polybrominated diphenyl ether congeners) in different biological treatment systems [activated sludge, up-flow anaerobic sludge blanket reactor (UASB) and waste stabilization pond (WSP)] was investigated to provide insights into the limits of engineered biological treatment systems. This was done through degradation experiments with inhibition and abiotic controls in static reactors under aerobic and anaerobic conditions. Estrogens showed higher first order degradation rates (0.1129 h−1) under aerobic conditions with activated sludge inocula followed by low molecular weight (LMW) PAHs (0.0171 h−1), triclosan (0.0072 h−1), middle (MMW) (0.0054 h−1) and high molecular weight PAHs (HMW) (0.0033 h−1). The same trend was observed under aerobic conditions with a facultative inoculum from a WSP, although at a much slower rate. Biodegradation was the major removal mechanism for these chemicals in the activated sludge and WSP WWTPs surveyed. Photodegradation of these chemicals was also observed and varied across the group of chemicals (estrogens (light rate = 0.4296 d−1; dark = 0.3900 d−1) degraded faster under light conditions while reverse was the case for triclosan (light rate = 0.0566 d−1; dark = 0.1752 d−1). Additionally, all the chemicals were resistant to anaerobic degradation with UASB sludge, which implies that their removal in the UASB of the surveyed WWTP was most likely via sorption onto solids. Importantly, the first order degradation rate determined in this study was used to estimate predicted effluent concentrations (PECs). The PECs showed good agreement with the measured effluent concentrations from a previous study for these treatment systems.

A COMPREHENSIVE ASSESSMENT OF SEPTAGE MANAGEMENT IN BANTUL, YOGYAKARTA

Aim: This study aims to assess the entire process of septage management comprising regulation, operational procedures, finance, community involvement, and water quality analysis to maximize the initial and hugest human fecal sludge treatment called Faecal Sludge Treatment Plant (IPLT) in Yogyakarta. Methodology and Results: The Modified EHRA (Environmental Health Risk Assessment) method was applied which focused only on wastewater treatment aspect. Several regulations including standard quality methods (SNI) were utilized and made a comparison between baseline rules and obtained results. Furthermore, quality assessment was accomplished by observation and interview. The results showed that the human sector needs to improve not only the amount of operators but also urgently put up protective personal equipment during the suction process. The dissemination of attractive information about sludge suction service done by PUPKP as a representation of the local government among the dwellers ought to upgrade a lot. Technologies employed which are carriage transportation and vacuum machine, are good enough. Contrarily, septage treatment plants require extra-effort to enhance it as most water quality parameters barely meet the standard quality. BOD, COD, ammonia, total coliform, oil and grease do not meet the third class of water quality (Government Regulation of Republic of Indonesia No. 82/2001). Subsequently, the effectiveness of each unit i.e. anaerobic tank and stabilization ponds are under 50% and the loading rate has a maximum capacity of 87.5m3/day, and 60m3/day minimum capacity. Conclusion, significance and impact of study: Therefore, almost all aspects of septage management in Bantul Yogyakarta are required to improve

Behavior and Removal of Ciprofloxacin and Sulfamethoxazole Antibiotics in Three Different Types of Full-Scale Wastewater Treatment Plants: A Comparative Study

Due to the inadequate removal rates of drug residues in wastewater treatment plants (WWTP), the transition of these compounds into the environment has become a serious environmental problem for ecosystems and public health. In this study, occurrence, fate, and removal of widely consumed two antibiotics, ciprofloxacin (CIP) and sulfamethoxazole (SMX), selected from fluoroquinolone and sulfonamide groups, respectively were investigated in three different types of full-scale WWTPs located in Turkey. In this context, three WWTPs consisting of advanced biological treatment (large-scale), wastewater stabilization pond (WSP) (medium-scale), and constructed wetland (CW) (small-scale) were selected. While the detected influent concentrations of CIP in WWTPs ranged between the 218.6 and 2733.5 ng/L, maximum influent concentration for SMX in the same plants was determined as 179.7 ng/L. On the other hand, although it was detected at higher concentrations in raw wastewater, CIP was significantly removed in all WWTPs with a removal efficiency ranging from >77.1 to >98.2%. However, SMX showed quite different behaviors depending on the applied wastewater treatment processes in WWTPs in terms of total removal achieved. While treated in WSP well enough (>72.2%), a serious negative removal efficiency (−133.4%) was achieved for SMX in the WWTP having advanced biological treatment. Best removal performance obtained for the both antibiotic compounds among the investigated WWTPs was the medium-scale WSP consisting of anaerobic and facultative stabilization ponds, consecutively. This situation also supported the idea that WWTPs which are operated with higher solid retention time (SRT) and hydraulic retention time (HRT) contribute positively in the removal of antibiotic compounds.

Occurrence, fate and environmental risk of anionic surfactants, bisphenol A, perfluorinated compounds and personal care products in sludge stabilization treatments

In this work, twenty-three endocrine disrupting compounds have been monitored in sludge from different stages of four sludge stabilization treatments (anaerobic digestion, aerobic digestion, composting and anaerobic stabilization ponds). Their occurrence and fate in sludge stabilization plants and their potential environmental risk in treated sludge and in treated sludge-amended soils have been evaluated. Monitored compounds were six perfluoroalkyl compounds (PFC), four anionic surfactants (sodium alkylsulfates), a plasticiser (bisphenol A (BPA)), four preservatives (parabens), six UV-filters (benzophenones) and two biocides (triclosan and triclocarban). Only two of the UV-filters were not detected in any of the 141 analysed samples. Anionic surfactants (mean concentrations up to 1673 ng/g dry matter (dm) for the sum of surfactants) were the compounds at the highest concentration levels followed by biocides (up to 512 ng/g dm) and UV-filters (up to 662 ng/g dm). The concentrations of anionic surfactants, preservatives and UV-filters decreased 78, 25 and 80%, respectively, after anaerobic digestion. The concentration of perfluorinated carboxylic acids only decreased after composting (80% reduction) whereas biocides and BPA were not affected by any of the studied treatments. Environmental risks (risk quotients > 1) were obtained for all compounds, except for triclocarban and sodium octadecylsulfate, in treated sludge. In treated sludge-amended soils, risk quotients were lower than 1 for all compounds except for triclosan.

EFFECT OF MOLASSES ADDITION AS BIODEGRADABLE MATERIAL ON PHENOL REMOVAL UNDER ANAEROBIC CONDITIONS

The link between the concentration of biodegradable organic matter and the rate of phenol removal in anaerobic conditions was examined in this work. This study was undertaken using a laboratory scale anaerobic stabilization pond and five closed reactors at two retention times, 2 and 5 days. The initial concentration of phenol and soluble COD decreased in the anaerobic pond effluent and the reactors with increasing hydraulic retention time; 98.6 % phenol removal was observed in reactors after 50 days and in the presence of 1000 mg/L COD, while 98.8 % removal was obtained after 5 days in the anaerobic stabilization pond system in the presence of 500 mg/L COD. Two-way ANOVA test with Scheffe post-hoc confirmed that phenol removal was optimal for 1000-2000 mg/L biodegradable COD and 50 days retention time in the reactors and with 500 mg/L biodegradable COD and 5 days retention time in the anaerobic pond.

Evaluation of anaerobic stabilization pond for removal of pentachlorophenol from wastewater: response surface methodology

Evaluation of anaerobic stabilization pond for removal of pentachlorophenol from wastewater: response surface methodology

Removal of organic matter and ammoniacal nitrogen from landfill leachate using the UV/H2O2 photochemical process

ABSTRACTThis study investigates the effects of pH, H2O2 concentration and reaction time of the UV/H2O2 photochemical process on the removal of organic matter and ammonia from biologically pre-treated landfill leachates in anaerobic stabilization ponds. The results show that the concentration of H2O2 and the initial pH are significant factors, with no significant interaction between them. A pH of 3 is the optimum value for the UV/H2O2 process for the removal of organic matter, resulting in 51.63% chemical oxygen demand (COD) removal in addition to the removal of aromatic compounds. The N-NH3 removal showed little variation between pH values of 1, 5, 7, 11 and 13; the removal was on the order of 16.43 ± 2.00%. The consumption of H2O2 was elevated at pH 9, 11 and 13; at these pH values, the average removal was 94.56 ± 0.43%, compared to 43.07% at pH 3. First-order polynomial models and reaction times on the order of 15 min are sufficient for optimization studies and for evaluation of the effects of the studied parameters. The results of this study support the optimization of the UV/H2O2 process for the removal of organic matter and ammonia from landfill leachates.

Phenol removal from oil refinery wastewater using anaerobic stabilization pond modeling and process optimization using response surface methodology (RSM)

Oil refinery process releases toxic pollutants into aqueous environment. Phenol and its derivations as the most important pollutants pose severe environmental concern. In this study, the rectangle anaerobic stabilization pond (ASP) consisting of feed tank with workload of 60 Lit (1 × 0.2 × 1) meter of phenol was used. This study evaluated the interactive effect of phenol concentration (200–400 mg/l), temperature (8–24°C) and Hydraulic retention time of (HRT) (2–5 d) on the efficiency of anaerobic stabilization pond for oil refinery wastewater treatment. In this study, experiments were carried out based on central composite design (CCD) and analyzed and modeled by response surface methodology (RSM) aimed at demonstrating the operating variables and also the interactive effect of three independent variables on 7 responses. The maximum removal efficiency of SCOD, TCOD, SBOD and TBOD were 66.26, 68.95, 65.3 and 67.02, respectively, at phenol concentration of 200 mg/L, HRT of 2 d, and temperature of 24°C. Generally, the ratio of N/P varied between 6.69–9.12 and 7.04–12.93, respectively, in influent and effluent of anaerobic stabilization pond. The maximum phenol removal efficiency reached 70.53 and 81.63 at phenol concentration of 200 mg/L, temperature of 24°C with HRT (2 and 5 d), respectively. The phenol removal efficiency was significantly influenced by increasing the temperature compared to decreasing the phenol concentration. The result indicated that the anaerobic stabilization pond was a capable biological treatment process that could achieve the moderate removal of oil refinery wastewater. © 2017 Desalination Publications. All rights reserved.

Latitudinal distribution of microbial communities in anaerobic biological stabilization ponds: effect of the mean annual temperature.

SummaryConsidering wide utilization and high methane fluxes from anaerobic biological stabilization ponds (ABSPs), understanding the methanogenesis in ABSPs is of fundamental importance. Here we investigated the variation and impact factors of methanogenesis in seven ABSPs that spanned from the north to the south of China. Results showed that methanogen abundance (7.7 × 109–8.7 × 1010 copies g−1 dry sediment) and methanogenic activities (2.2–21.2 μmol CH 4 g−1 dry sediment h−1) were considerable for all sediments. Statistical analysis demonstrated that compared with other factors (ammonium, pH, COD and TOC), mean annual temperature (MAT) showed the lowest P value and thus was the most important influencing factor for the methanogenic process. Besides, with the increasing MAT, methanogenic activity was enhanced mainly due to the shift of the dominant methanogenic pathway from acetoclastic (49.8–70.7%) in low MAT areas to hydrogenotrophic (42.0–54.6%) in high MAT areas. This shift of methanogenic pathway was also paralleled with changes in composition of bacterial communities. These results suggested that future global warming may reshape the composition of methanogen communities and lead to an increasing methane emission from ABSPs. Therefore, further research is urgently needed to globally estimate methane emissions from ABSPs and re‐examine the role of ABSPs in wastewater treatment.

Characterization and evaluation of treatability of wastewater generated in Khuzestan livestock slaughterhouses and assessing of their wastewater treatment systems

&lt;div&gt; &lt;p&gt;Slaughterhouse wastewaters are characterized by a high organic content, mainly composed of proteins and fats. Therefore, these wastewaters should be treated efficiently prior to discharge into receiving bodies to avoid severe environmental pollution. This work aimed to characterize slaughterhouse wastewater generated in one province of Iran (Khuzestan), evaluating various suitability of biological treatment, assessing wastewater treatment plants performance and feasibility of wastewater reuse. Composite samples were collected from input and output of wastewater treatment plant during 6 months (spring and summer) and were analyzed for TSS, turbidity, temperature, conductivity, pH, COD, BOD&lt;sub&gt;5&lt;/sub&gt;, fat, total coliform and fecal coliform. Data analysis was done using Excel and SPSS software. The results showed that different quantities of wastewater were generated in any slaughterhouses of Ahvaz (120-600 l/d.sheep), Dezful (110-550 l/d.sheep), and Shushtar (139-694 l/d.sheep). Khuzestan slaughterhouses wastewater is classified by pollution severity as strong wastewater. The BOD&lt;sub&gt;5&lt;/sub&gt;/COD ranges from 0.3 to 0.5, which indicates applicability of biological treatment. Wastewater treatment plant of Ahvaz with anaerobic stabilization ponds and extended aeration activated sludge process has the highest removal efficiencies of pollutants. The result also indicated reuse of slaughterhouses effluent was not acceptable due to not comply with the standards of Iran. Finally, if safe use or disposal of these effluents is desired, blood capture from raw wastewater for reducing the amounts of organic loading must be implemented. Also, use of an appropriate treatment plant is noted.&lt;/p&gt; &lt;/div&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Pharmaceutically active compounds in sludge stabilization treatments: Anaerobic and aerobic digestion, wastewater stabilization ponds and composting

Sewage sludge disposal onto lands has been stabilized previously but still many pollutants are not efficiently removed. Special interest has been focused on pharmaceutical compounds due to their potential ecotoxicological effects. Nowadays, there is scarce information about their occurrence in different sludge stabilization treatments. In this work, the occurrence of twenty-two pharmaceutically active compounds has been studied in sludge from four sludge stabilization treatments: anaerobic digestion, aerobic digestion, composting and lagooning. The types of sludge evaluated were primary, secondary, anaerobically-digested and dehydrated, composted, mixed, aerobically-digested and dehydrated and lagoon sludge. Nineteen of the twenty-two pharmaceutically active compounds monitored were detected in sewage sludge. The most contaminated samples were primary sludge, secondary sludge and mixed sludge (the average concentrations of studied compounds in these sludges were 179, 310 and 142μg/kgdm, respectively) while the mean concentrations found in the other types of sewage sludge were 70μg/kgdm (aerobically-digested sludge), 63μg/kgdm (lagoon sludge), 12μg/kgdm (composted sludge) and 8μg/kgdm (anaerobically-digested sludge). The antibiotics ciprofloxacin and norfloxacin were found at the highest concentration levels in most of the analyzed sludge samples (up to 2660 and 4328μg/kgdm, respectively). Anaerobic-digestion treatment reduced more considerably the concentration of most of the studied compounds than aerobic-digestion (especially in the case of bezafibrate and fluoroquinolones) and more than anaerobic stabilization ponds (in the case of acetaminophen, atenolol, bezafibrate, carbamazepine, 17α-ethinylestradiol, naproxen and salicylic acid). Ecotoxicological risk assessment, of sludge application onto soils, has also been evaluated. Risk quotients, expressed as the ratio between the predicted environmental concentration and the predicted non-effect concentration, were lower than 1 for all the pharmaceutically active compounds so no significant risks are expected to occur due to the application of sewage sludge onto soils, except for 17α-ethinylestradiol when chronic toxicity was considered.

Water treatment plant sludge disposal into stabilization ponds

Researchers have paid particular attention to the disposal of sludge produced in water treatment plants (WTPs) into wastewater treatment plants (WWTPs) for further processing, mainly because it is considered an attractive alternative for the treatment of waste generated in water production processes. This study evaluated the effects of flow equalization and disposal of sludge, from a conventional WTP, into a WWTP system that includes an anaerobic stabilization pond followed by a facultative pond. During the period of sludge discharge from the WTP into the wastewater system, the influent to the WWTP presented an increase of 17% (from 171 to 200 mg L(-1)) of total suspended solids (TSS) and a 7.0% flow rate increase, without showing adverse effects on the organic load, TSS and nutrients removal. The most significant impact observed in the WWTP was the increase of solids accumulation rate in the anaerobic pond, with a value of 141 mm/year during the sludge discharge period. The operating time, before the dredging and desludging cycles required for this specific anaerobic pond, decreased from 12.7 to 10.4 years, which is consistent with previous studies in literature. Thus, based on the observed parameters of this study, it is viable to release solids from a WTP effluent into a WWTP that includes anaerobic stabilization ponds followed by a facultative pond. Indeed, this process scheme becomes a viable technical, environmental, and economical alternative for small to medium WWTPs.

Start-up Operation of Anaerobic Degradation Process for Palm Oil Mill Effluent in Anaerobic Bench Scale Reactor (ABSR)

The start-up operation or acclimatization process of anaerobic stabilization pond treatment for palm oil mill effluent (POME) was carried out in a laboratory anaerobic bench scale reactor (ABSR). The start-up operation of the ABSR was operated at two different organic loading rates (ORG) of 0.89 – 0.92 kg COD/m3/day and 1.34 – 1.37 kg COD/m3/day which corresponds to hydraulic retention time (HRT) of 60 and 40 days. The investigation showed that the acclimatize process for anaerobic degradation of POME was completed after 48 days of operation. In present study, the indicators that been used were pH, microbial growth, effluent of total chemical oxygen demand (COD), COD removal efficiency, alkalinity and ratio fraction between volatile fatty acid and alkalinity.

Occurrence and risk assessment of nonylphenol and nonylphenol ethoxylates in sewage sludge from different conventional treatment processes

In the present work, the concentrations of the organic pollutants nonylphenol (NP) and nonylphenol mono- and diethoxylates (NP1EO and NP2EO, respectively) in primary, secondary, mixed, aerobically-digested, anaerobically-digested, dehydrated, compost and lagoon sludge samples from different sludge treatments have been evaluated. Toxicological risk assessment of these compounds in sludge and sludge-amended soil has also been reported. NP, NP1EO and NP2EO were monitored in sludge samples obtained from treatment plants located in Andalusia (south of Spain) based on anaerobic treatments (11 anaerobic-digestion wastewater treatment plants and 3 anaerobic wastewater stabilization ponds) or on aerobic treatments (3 aerobic-digestion wastewater treatment plants, 1 dehydration treatment plant and 2 composting plants). The sum of NP, NP1EO and NP2EO (NPE) concentrations has been evaluated in relation to the limit value of 50 mg/kg set by the European Union Sludge Directive draft published in April 2000 (Working Document on Sludge). In most of the samples, NP was present at higher concentration levels (mean value 88.0 mg/kg dm) than NP1EO (mean value 33.8 mg/kg dm) and NP2EO (mean value 14.0 mg/kg dm). The most contaminated samples were compost, anaerobically-digested sludge, lagoon sludge and aerobically-digested sludge samples, which contained NPE concentrations in the ranges 44–962 mg/kg dm, 8–669 mg/kg dm, 27–319 mg/kg dm and 61–282 mg/kg dm, respectively. Risk quotients, expressed as the ratios between environmental concentrations and the predicted no-effect concentrations, were higher than 1 for NP, NP1EO and NP2EO in the 99%, 92% and 36% of the studied samples, respectively; and higher than 1 in the 86%, 6% and 2%, respectively, after sludge application to soil, leading to a significant ecotoxicological risk mainly due to the presence of NP.

Biological kinetics evaluation of anaerobic stabilization pond treatment of palm oil mill effluent

Biological kinetic (bio-kinetic) study of the anaerobic stabilization pond treatment of palm oil mill effluent (POME) was carried out in a laboratory anaerobic bench scale reactor (ABSR). The reactor was operated at different feed flow-rates of 0.63, 0.76, 0.95, 1.27, 1.9 and 3.8 l of raw POME for a day. Chemical oxygen demand (COD) as influent substrates was selected for bio-kinetic study. The investigation showed that the growth yield ( Y G ), specific biomass decay ( b), maximum specific biomass growth rate ( μ max), saturation constant ( K s ) and critical retention time ( Θ c ) were in the range of 0.990 g VSS/g COD removed day, 0.024 day −1, 0.524 day −1, 203.433 g COD l −1 and 1.908 day, respectively.

Presence of organic pollutants in sludge from anaerobic wastewater stabilization ponds

One of the most common disposal options of sewage sludge is its application to agricultural lands. During wastewater treatments, pollutants tend to be concentrated into sludge so it is important to evaluate the concentration of those pollutants to avoid negative effects to the environment. To control the quality of the sludge that is going to be applied to soil, the European Union (EU) published in 2000 the third draft of a future sludge Directive entitled “Working Document on Sludge” where concentration limit values for some organic compounds (AOX, DEHP, LAS, NPE, PAH, PCB and PCDD/F) are fixed. The implementation of the future Directive could imply the application of post-treatment processes to sludge to reduce the concentration levels of the organic pollutants to levels that enable safe application of sewage sludge as soil fertilizer. Several authors have reported concentration levels of the above cited pollutants in anaerobic and aerobic treatment plants. However, there is no much information about concentration levels in lagoon sludge from anaerobic wastewater stabilization ponds which are the most common wastewater treatments applied in small communities with equivalent inhabitants in the range up to 10,000. In the present work, concentration levels of several of the organic compounds included in the EU directive draft have been measured in sewage sludge samples from three wastewater stabilization ponds operating in small communities located in the south of Spain. Organic compounds measured were di- (2-ethylhexyl)phthalate (DEHP), sum of nonylphenol and nonylphenol ethoxylates with 1 and 2 ethoxy groups (NPEs), linear alkylbenzene sulphonates (LAS), sum of nine polycyclic aromatic hydrocarbons (PAHs) and sum of seven polychlorinated byphenyls (PCBs). Sludge applicability to soil, in relation with the limit values fixed in the EU sludge directive draft, has been evaluated. The highest concentration levels were found for LAS (mean value 5373 mg/kg dry matter), NPE (mean value 177.1 mg/kg dry matter) and DEHP (mean value 72.3 mg/kg dry matter), in this order. PAHs were detected at lower concentration levels (concentrations lower than 0.80 mg/kg dry matter) whereas no PCB was detected in the analyzed samples.